CBSE Class 7 Science Chapter 13 Wastewater Story — 20 MCQs with Answers

Sewage is the liquid waste generated by homes, hospitals, industries, and offices. It consists of water mixed with dissolved and suspended impurities — organic matter like human waste and food residues, inorganic substances such as nitrates and phosphates, nutrients, bacteria, and other microorganisms. The NCERT text emphasises that sewage is approximately 99.9 percent water by weight; the remaining 0.1 percent comprises suspended solids and dissolved chemicals. Grasping the difference between sewage and sewerage (the infrastructure of pipes and pumps) is fundamental. These MCQs test your knowledge of sources, composition, and the terminology used in the chapter.

Wastewater treatment plants (WWTPs) clean sewage through three main stages. Physical treatment involves screening and sedimentation to remove large solids and grit. Biological treatment uses aerobic bacteria to decompose organic matter in aeration tanks; the microbes digest waste, reducing its toxicity. Chemical treatment includes chlorination to kill remaining pathogens before the treated water is released into rivers or seas. Sludge — the solid waste that settles — is transferred to a separate tank where anaerobic bacteria break it down, producing biogas (mainly methane). The dried sludge can be used as manure. These MCQs assess your understanding of each treatment stage and the role of microorganisms.

Poor sanitation and untreated sewage are direct causes of water-borne diseases. When sewage contaminates drinking water sources, pathogens like bacteria, viruses, and protozoa spread rapidly. Diseases such as cholera, typhoid, hepatitis A, and dysentery are common in areas with inadequate sewerage and open defecation. The NCERT chapter stresses that proper sanitation — toilets, sealed drains, and regular garbage collection — is a basic human right and a public health necessity. Access to clean drinking water and hygienic waste disposal prevents epidemics and improves community well-being. These MCQs focus on the link between sanitation, disease transmission, and preventive measures.

The NCERT chapter emphasises that each household can reduce the burden on sewerage systems by adopting better practices. Do not pour cooking oil or fats down the drain — they solidify and clog pipes. Avoid flushing chemicals, medicines, sanitary napkins, or solid waste into toilets; these items do not decompose and can damage treatment plants. Use dustbins for garbage and minimise water wastage. Composting kitchen waste reduces organic load on sewage. Educating family members about these habits contributes to community hygiene and environmental protection. These MCQs test your grasp of responsible waste disposal and eco-friendly habits at home.

Beyond direct recall, CBSE exams often include application-based and assertion-reason questions that test deeper understanding. You might be asked to analyse a scenario — for example, predicting the effect of untreated sewage on a lake's dissolved oxygen, or comparing the environmental impact of different waste disposal methods. HOTS questions require you to connect chapter concepts with real-world problems, such as water scarcity, pollution control, and sustainable sanitation. These MCQs mirror the difficulty level of CBSE sample papers and help you prepare for tricky questions that demand reasoning rather than rote memory.

Multiple-choice questions in CBSE Class 7 Science papers typically carry 1 mark each and test recall, application, and reasoning. Start by reading each question carefully — note keywords like 'NOT', 'BEST', or 'LEAST', which can change the correct answer. Eliminate obviously wrong options first; if two options seem correct, re-read the question stem and match it against NCERT definitions. For assertion-reason questions, check whether both statements are true individually, then decide if the reason correctly explains the assertion. Manage your time: spend no more than 30–40 seconds per MCQ. If stuck, mark the question and return after completing easier ones. Practising 20–30 MCQs daily from each chapter builds speed and confidence. Use CBSETUTOR.ai to upload screenshots of tricky MCQs and get instant step-by-step explanations — at ₹999 per month for Classes 6–12, you get a 24×7 AI tutor with photo-solving and doubt-clearing, plus a 3-day free trial to explore the platform risk-free.